Effects of cold fronts on MODIS-derived sensible and latent heat fluxes in Itumbiara reservoir (Central Brazil)

Abstract

In this work we investigate the cold front passage effects on sensible and latent heat flux in a tropical hydroelectric reservoir. The study area, Itumbiara reservoir (Goiás State/Brazil) at the beginning of the austral winter, is characterized by the presence of a weak thermal stratification and the passage of several cold fronts from higher latitudes of South America. Sensible and latent heat fluxes were estimated considering the atmospheric boundary layer stability. In situ and MODIS water surface temperature data were used to adjust the coefficients for momentum and heat exchanges between water and atmosphere and spatialize the sensible and latent heat fluxes. The results showed that during a cold front event the sensible heat flux can be up to five times greater than the flux observed before. The latent heat flux tends to decrease during the cold front but increase again after the passage. The highest values of heat loss were observed at littoral zone and some Reservoir’s embayment. The heat loss intensification can be separated in two moments: first, during the cold front passage, when the wind speed increases and the air temperature decreases; second, after the cold front passage, with air humidity decreasing. This can be considered a key process to understanding the heat loss in the Itumbiara reservoir.